Deicers
The presence of ice and snow on pavement such as roads, sidewalks, bridges, runways, and the like presents safety hazards and operational obstacles to many everyday activities such as driving, flying, etc. Over the years, a variety of techniques have been used in the colder parts of the world to remove or destroy ice and snow. The techniques utilized have ranged from simple mechanical approaches (e.g., shoveling or plowing) to heating (e.g., by means of buried heating elements or by the direct application of heat) to chemical methods (e.g., the use of deicers such as sodium chloride and calcium chloride in solid or solution form). Where large surface areas and large accumulations of ice and snow are involved, such as roadways and runways, a combination of mechanical (e.g., snowplowing) and chemical methods (e.g., salt mixed with sand) are commonly used.
The most commonly used chemical deicer for highways is sodium chloride in the form of rock salt. Sodium chloride is used since it is relatively inexpensive, readily available in large quantities, and weight efficient as a deicer. At the present time it is estimated that the U.S.A. alone uses about 9 to 10 million tons of salt each year for deicing purposes. It is generally agreed that calcium chloride is the most effective chemical now used as a bulk deicer on a weight for weight basis. However calcium chloride is a relatively expensive chemical commodity and, like sodium chloride, is a source of chloride ion, an active corrosion agent.
In recent years, increasing attention has been focused on the total economic impact of the use of sodium chloride (i.e., rock salt) or calcium chloride or mixtures thereof as a highway deicing chemical and it has been discovered that while the initial cost of sodium chloride or calcium chloride is relatively low, the total cost can be enormous. Consideration must be given to the corrosive damage to vehicles and pavement, the corrosive damage to metal structures such as bridge elements and highway reinforcing bars, and environmental damage to soil, water, plants and animals. By way of illustration, the U.S. Environmental Protection Agency published data in 1976 suggesting that the conservative cost of the damage resulting from the use of sodium chloride-rock salt for highway deicing is approximately fifteen times the direct cost of purchasing and applying the salt in the first instance. Against this background, the State of South Dakota has already limited future use of sodium chloride salt for highway deicing purposes; and other political bodies may take similar actions in the future.
With these economic incentives, new research interest has been directed toward the idea of developing alternative deicing chemicals that would have a total cost (e.g., on a state-wide basis) which would be significantly less than the total cost associated with the use of sodium chloride or calcium chloride as a highway deicer. However, if the highway community is to be provided with an effective, non-corrosive, environmentally acceptable chemical deicer, it is necessary to develop commercially attractive production methods. Processes must be found that can be operated economically, producing the deicing product at an acceptable cost. To reduce transportation costs, it would be desirable to manufacture the deicing product in the geographic area where the deicing chemical is to be used and to produce the chemical from biomass materials found in the area.
Against this background, there has been renewed interest in the possible use of a generally equimolar mixture of calcium and magnesium acetates, commonly referred to as "CMA", which has shown considerable promise as a deicing chemical. Limited field tests have confirmed its ability to function as a deicer. Moreover, CMA does not contain the chloride ion present in sodium chloride, which is apparently responsible for many corrosive side effects. However, CMA is expensive to manufacture if it is prepared by classical chemical methods using relatively pure chemicals. Consequently, some suggestions have been made that a less pure form of acetic acid might be used in an effort to reduce the cost of making CMA and some consideration has been given to the possibility of producing CMA by a process in which a crude form of acetic acid is made by reacting cellulose with an inorganic base at atmospheric pressure. For example, it is known that acetic acid can be made by fusing sodium hydroxide with cellulosic materials to provide yields of acetic acid of about 15 percent. However, it has been noted that the production of large amounts of acetic acid by this route is accompanied by the production of significant amounts of oxalic acid.